抄録
Since the discovery of two endogenous opioid peptides, Met-and Leu-enkephalins, a lot of works have been done to develop better analgesics without side-reactions. By now many highly potent analogues of enkephalins have been designed and synthesized. But, pure analgesics have not so far been obtained. It is mainly because of the complexity of opioid ligands and their interactions with multiple receptors. In addition recent knowledge of enhancing effects of peptidase inhibitors on the potency of opioid peptides prompts us to reexamine all the accumulated pharmacological data.
